This invention relates to a method of and apparatus for providing an indication of the position of a valve member in a fluid path.
Rotary and linear moveable valve members are well known for controlling the pressure and flow of fluid, such as air, in fluid systems.
In one exemplary application of the present invention, in an aircraft, pressurised air may be bled from one or more aircraft engine, for use in an air-conditioning system or an anti-icing system, for examples only. The air flow from the engine or engines is controlled by a valve which has a moveable valve member, such as a rotary butterfly valve member or a linearly acting valve member, which valve is power operated under the control of a controller, which may be a dedicated valve controller, or part of a more general control system.
In an aircraft, there is an airworthiness requirement that an indication may be given e.g. to a pilot, as to whether the valve member is closed or open. Conventionally this is established by the provision of one or more micro-switches read switches or proximity switches, located such that the switch is or switches are operated as the valve member moves to a fully open and/or fully closed position, but such switches require a switchable source of electrical power to operate.
From the point of view of switch sensitivity, an ideal position to locate such switches is close to an operating arm which is carried by and hence located close to the valve member. Such a prior art arrangement is indicated in the drawing and is described briefly below with reference to the drawing.
Particularly in use in a fluid path for hot engine bleed air in an aircraft, in this position, the switch(es) is/are subjected to substantial heat, possibly up to or in excess of 500° C., at which temperature, the performance of the switch can adversely be affected. Also, whereas butterfly/linearly acting valves may be designed to be sufficiently robust to withstand repeated valve member movement and at high speed in such harsh environment, switches are less tolerant. Switches are also not inexpensive to provide and maintain.